Sulfoxide derivatives have attracted attention in the field of agricultural chemicals etc. (see Patent document 1). It is therefore important that sulfoxide derivatives are produced selectively and in high yields. Oxidation of sulfide derivatives is known as a method for producing sulfoxide derivatives. However, in general, this method has a problem that a sulfone derivative which is an excessively oxidized product is by-produced. The unnecessary by-produced sulfone derivative lowers the yield of the desired sulfoxide derivative. Furthermore, since the physical properties of both derivatives are similar, it is difficult to obtain a purified target sulfoxide derivative in the industrial production by removing the byproduct sulfone derivative from the crude product after the oxidation reaction. That is to say it is difficult to separate and purify the target product with high yield on an industrial scale. Accordingly, it has been desired to be able to selectively produce sulfoxide derivatives by avoiding excessive oxidation to sulfone derivatives.
Patent Document 1 discloses that a sulfoxide derivative can be produced by an oxidation reaction with metachloroperbenzoic acid (See, for example, Examples 13 and 27 of Patent Document 1). However, considering the environmental aspect, the use of metachloroperbenzoic acid is not favorable for industrial production. The reasons are as follows. After the reaction, the metachloroperbenzoic acid becomes methachlorobenzoic acid as a waste. As a result, the use of metachloroperbenzoic acid places a heavy burden on the environment. In addition, since metachloroperbenzoic acid is expensive, the method of using metachloroperbenzoic acid is industrially undesirable.
On the other hand, oxidation using hydrogen peroxide is an industrially preferable and useful method. The reasons are as follows. Since hydrogen peroxide becomes harmless water after the reaction, it is environmentally friendly. Furthermore, hydrogen peroxide is industrially cheap.
Non-patent document 1 discloses asymmetric oxidation from a sulfide derivative to an optically active sulfoxide derivative. Non-Patent document 1 discloses a method using a Schiff base, which is conventionally known as a ligand and a benzoic acid compound. It has also been reported that this method gives some yield. However, the method described in Non-Patent Document 1 requires further improvement in yield. In addition, Non-Patent Document 1 describes that the yield and the enantiomeric excess ratio change depending on the substituent of the aryl moiety of the arylalkyl sulfide derivative. However, Non-Patent Document 1 merely discloses the yield and the enantiomeric excess ratio when the substituent is limited. In other words, Non-Patent Document 1 does not disclose a method for producing titled compound of the present invention, by which titled compound of the present invention can be obtained in sufficient and satisfactory yield and the like.
From the viewpoints of yield and enantiomeric excess ratio, it has been reported that 4-methoxybenzoic acid alkali metal salt and 4-(N,N-dimethylamino) benzoic acid alkali metal salt are excellent as benzoic acid compounds. Furthermore, the Schiff bases of the ligands are reported as follows. Regarding the amine moiety of Schiff s base as a ligand, tert-leucinol was superior to valinol from the viewpoint of yield and enantiomeric excess ratio. Regarding the salicylaldehyde moiety of Schiff's base as a ligand, 3,5-diiodosalicylaldehyde and 3,5-dibromosalicylaldehyde were superior to unsubstituted salicylaldehyde from the same viewpoint as above (see Non-Patent document 1, Table 1). However, in the production of titled compound of the present invention, it has not been known whether these benzoic acid compounds and ligands have an industrially advantageous effect. Furthermore, from the viewpoint of difficulty of availability, difficulty in industrial production, and/or cost, the use of 3,5-diiodosalicylaldehyde as a salicylaldehyde moiety of Schiff s base as a ligand is industrially undesirable.